CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (10,970)	$ (9,031)
Other comprehensive income (loss):
Net change in unrealized gains on marketable securities, net of tax of $0 for the quarters ended March 31, 2020 and 2019	(311)	94
Foreign currency translation		78
Other comprehensive income (loss)	(311)	172
Comprehensive loss	(11,281)	(8,859)
Less comprehensive loss attributable to redeemable non-controlling interest:
Net loss attributable to redeemable non-controlling interest	(328)	(250)
Foreign currency translation attributable to redeemable non-controlling interest		38
Comprehensive loss attributable to redeemable non-controlling interest	(328)	(212)
Comprehensive loss attributable to BlackLine, Inc.	$ (10,953)	$ (8,647)